This invention relates generally to an improvement of a combined magnetic head for use in a tape recorder.
Conventionally known combined magnetic heads are shown in FIGS. 1(A) and 1(B) and FIGS. 2(A) and 2(B). FIGS. 1(A) and 1(B) are a plane view and a front view, respectively, showing one example of the combined magnetic head, wherein a magnetic tape (not shown) tightly contacts and slidingly travels past tape sliding surfaces 1b and 2b. The combined magnetic head has two head units 1 and 2 [FIG. 1(B)], with the head unit 1 including a magnetic core 1a and tape sliding surface 1b while the head unit 2 includes a magnetic core 2a and tape sliding surface 2b . These two head units 1 and 2 are magnetically shielded by a shielding plate 3. The head units 1 and 2 and the shielding plate 3 are accommodated into a single head case, thereby forming the combined magnetic head.
FIGS. 2(A) and 2(B) are a plane view and a front view, respectively, showing another example of a prior art combined magnetic head, wherein the magnetic tape slidingly contacts and travels past tape sliding surfaces 5b and 6b. The combined magnetic head has two head units 5 and 6 [FIG. 2(B)], with the head unit 5 including a magnetic core 5a and tape sliding surface 5b while the head unit 6 includes a magnetic core 6a and tape sliding surface 6b. The head units 5 and 6 are accomodated into the respective head cases 5c and 6c. These two head cases 5c and 6c adjoin each other and are combined to form the combined magnetic head.
While the advantages of a combined magnetic head are well known, for example, the running distance of the magnetic tape is shortened, the tape running is stabilized, and adjustment of installing respective heads is unnecessary because they are integrally formed and can be treated in the same manner as in the case of a single magnetic head, it's disadvantages such that at the time of simultaneous monitoring, a signal of a recording head interfers a reproducing signal of a reproducing head, i.e. so-called "cross feed" phenomena, are equally appreciated.
The combined magnetic head as shown in FIGS. 1(A) and 1(B) is advantageous in that it prevents cross feed. According to this structure, however, the relationship between the configuration of the cores 1a and 2a and the contact of the magnetic tape thereto is degraded resulting that frequency response curves at the region of less than 1 KHz become corrugated and thus contour characteristics are degraded.
On the other hand, the magnetic head shown in FIGS. 2(A) and 2(B) is advantageous in terms of contour characteristics whereas it is disadvantageous in terms of cross feed as compared with the magnetic head shown in FIGS. 1(A) and 1(B). Further, stable tape running cannot be achieved per se according to the magnetic head shown in FIGS. 2(A) and 2(B), especially in a cassette tape recorder in which a tape pressure pad is employed, since a recessed wedge shaped portion is formed at the center of the tape sliding surfaces 5b and 6b. Specifically, due to scattering of the tape pressure pad in its pressing force (i.e. the force is not uniformly applied), rattling of the fixed portions of the pressure pad and the difference in the pad material, the magnetic tape vibrates in directions indicated by arrows 8 when the tape travels past the heads. Hence, the contact of the magnetic tape to the sliding surfaces 5b and 6b becomes unstable. If the contact of the magnetic tape to the sliding surfaces of the magnetic head becomes unstable, various kinds of unwanted losses, such as tracking loss, azimuth loss, etc. are increased. As a result, an electro-magnetic conversion would be implemented in a distorted fashion with the attendant loss of sound reproduction.
In order to reduce or eliminate the above-mentioned losses, it has been proposed to employ and auxiliary plate 9 whose cross-section is rectangular as shown in FIG. 3. The auxiliary plate 9 is provided so that both ends thereof are adjacent to the tape sliding surfaces 5b and 6b covering the wedge shaped open portion. The auxiliary plate 9 is made of non-magnetic material or soft magnetic material and is fixed to the head units 5 and 6 by an adhesion agent 10, such as an epoxy resin or the like. An improved structure and arrangement of the auxiliary plate is shown in FIG. 7 of co-pending application Ser. No. 957,503.
The condition of stable tape running can be achieved by contacting the magnetic tape not only to the sliding surfaces 5b and 6b but also to the sliding surface 9b of the auxiliary plate 9. As a result, the above-mentioned unwanted losses are reduced. However, it is still disadvantageous in that the tape tends to be damaged or injured and dust accumulates in the side portions 9a of the auxiliary plate 9. This is due to the fact that an angle .theta..sub.1 defined by the side edge 9a of the auxiliary plate 9 and the tape sliding surface 9b thereof is approximately 90.degree..